1. Field of the Invention
The present invention relates in general to an apparatus for interfacing between a mobile switching center and an inter working function unit (IWF) according to a frame relay protocol, and more particularly to an apparatus for interfacing between a mobile switching center and an IWF in a code division multiple access (CDMA) mobile telecommunications system, in which the mobile switching center is adapted to transfer a particular number of low-rate (for example, 8 Kbps) subscriber data to the IWF while mapping them into one trunk channel, thereby enhancing the utilization of the trunk channel.
2. Description of the Prior Art
Generally, in a radio data service network using a CDMA mobile telecommunications system, a new network known as an IWF network is further provided to smoothly perform a radio data service.
FIG. 1 shows the construction of a radio data service network of a general mobile telecommunications system in which an IWF network is newly provided as mentioned above. In this drawing, the reference numeral 1 denotes a personal computer (PC) for interfacing data with a mobile station (MS) 2, which, in turn, communicates data with a base transceiver station (BTS) 3 by radio. A base station controller (BSC) 4 is adapted to control the data communication of the BTS 3. A mobile switching center (MSC) 5 is adapted to switch data between specific mobile stations through the BSC 4. A CDMA network 6 is connected to the MSC 5 to communicate data with the MSC 5. A public switched telephone network (PSTN) 7 is connected to the MSC 5 to perform an analog voice telephone service. An IWF 10 is adapted to interface data with the MSC 5 through an IS-658 L interface. A packet switched and public data network (PSPDN) 8 and Internet 9 are connected to the IWF 10 to provide data and voice services.
In FIG. 1, the reference character Rm, not described, denotes an interface between the PC 1 and MS 2, Um denotes an interface between the MS 2 and BTS 3, A denotes an interface between the BSC 4 and MSC 5, Ai denotes an interface between the MSC 5 and PSTN 7, E denotes an interface between the MSC 5 and CDMA network 6 and Pi denotes an interface between the IWF 10 and PSPDN 8. Further, the reference numeral 11, not described, denotes a home location register (HLR).
In the general mobile telecommunications system with the above-mentioned construction, the PC 1 and MS 2 are interconnected via an RS-232C to interface data therebetween. The MS 2, in turn, communicates data and voice with the BTS 3 ia a radio interface (a transmission rate on the radio side: 8 Kbps) based on the IS-95 standard.
The BTS 3 communicates information of the BS 2 with the SC 4 via a wired interface and further transmits and receives voice and data to/from the BS 2 by radio via the IS-95 standard-based radio interface. That is, the BTS 3 handles a call control processing function, radio signal transmission/reception functions, a radio resource management function, a time information management function, error detection/statistical information collection/report functions, a packet routing function and a power control function.
The BSC 4 is located between the BTS 3 and MSC 5 to communicate data in the form of voice packets with the BTS 3 by wire and to perform a man-machine interface function for an operator interface and a global positioning system (GPS) reception function with the MSC 5. Namely, the BSC 4 handles an inter-mobile station call connection function, a handoff function when a mobile station moves from one sector to another sector in a base transceiver station or from a service area of a current base transceiver station to a service area of a different base transceiver station, a function of communicating voice and data information in the form of packets with a base transceiver station over a wired channel, a function of interfacing voice and signals with a mobile switching center, voice compression/restoration (transcoding) functions, a man-machine interface function for an operator interface, base transceiver station operation and construction management functions, and base station controller maintenance and fault management functions.
The MSC 5 performs interfacing operations with other MSCs, fixed subscribers and mobile telecommunication elements. Further, the MSC 5 performs inter working interfacing operations with other networks such as an integrated service digital network (ISDN) and public switched data network (PSDN). In the case where the MSC 5 includes an additional cellular gateway switching system function, it is implemented with a multiprocessor structure for distributing functions and loads. Such a multiprocessor structure is a two-step hierarchical, distributed control structure consisting of a master processor and slave processors.
On the other hand, in the general radio data service network construction as mentioned above, recently, the IWF 10 is newly provided to smoothly perform a radio data service.
As a result, there is a need for an interface to smoothly communicate voice and data between the MSC 5 and IWF 10.
A conventional interface between the MSC 5 and IWF 10 is based on an interface protocol defined in the IS-658 standard.
Further, the MSC 5 and IWF 10 transmit and receive data therebetween in a circuit switching manner or a packet switching manner. Information can be basically transferred at a rate of 64 Kbps in such a data transfer system. However, such a transfer rate may be an obstacle to the transfer of information in the packet switching manner due to a complexity in protocol.
A large amount of time is required for the transfer of a large amount of information in the case where such an obstacle is present or an information transfer rate per given time is low. A protocol newly proposed to overcome this problem is a frame relay protocol, which is able to interface high-rate data at the maximum rate of 2 Mbps.
However, in the case where the above data transfer system is directly applied to transfer data to a trunk, a channel utilization of the trunk will be degraded because a data transfer rate based on an inter-system link protocol (ISLP) between a base station controller and a mobile switching center is 8 Kbps.
In other words, in the case where the existing data transfer system is directly applied although the channel transfer rate of the trunk is 64 Kbps, it cannot help transferring data at a rate of 8 Kbps, resulting in the channel utilization of the trunk being reduced to xe2x85x9.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an apparatus for interfacing between a mobile switching center (MSC) and an inter working function unit (IWF) in a code division multiple access (CDMA) mobile telecommunications system, in which the MSC is adapted to transfer a large number of subscriber data to the IWF while mapping them into one trunk channel, thereby enhancing the utilization of the trunk channel.
In accordance with the present invention, the above and other objects can be accomplished by a provision of an apparatus for interfacing between a mobile switching center and an inter working function unit, comprising inter-system link protocol processing means for a) processing a plurality of subhighway data inputted respectively through subhighways in the unit of subscribers according to an inter-system link protocol; and b) separating data transferred over a given channel of an E1 trunk from the inter working function unit according to the subhighways and their time slots and transferring the separated data respectively to the subscribers; storage means for storing the subscriber-unit data processed by the inter-system link protocol processing means in the unit of channels or the data transferred over the given E1 trunk channel from the inter working function unit in the unit of the subscribers; and frame relay protocol processing means for a) extracting only a plurality of actual subscriber data from the channel-unit data stored in the storage means, processing the extracted actual subscriber data according to a frame relay protocol, assigning the processed actual subscriber data to a specific channel of the E1 trunk and transferring them to the inter working function unit; and b) extracting respective subscriber data from the data transferred over the given E1 trunk channel from the inter working function unit and storing the extracted subscriber data in the storage means in the unit of the subscribers.
Preferably, the inter-system link protocol processing means includes a high-level data link controller for formatting the plurality of subhighway data into a high-level data link control format, separating the data transferred over the given E1 trunk channel from the inter working function unit according to the subhighways and their time slots and transferring the separated data respectively to the subscribers via the subhighways; and an inter-system link protocol processor for processing the subhighway data formatted by the high-level data link controller according to the inter-system link protocol, storing the processed subhighway data in the storage means, reading the respective subscriber data from the frame relay protocol processing means from the storage means and outputting the read subscriber data to the high-level data link controller.
Preferably, the frame relay protocol processing means includes a frame relay protocol processor for reading the inter-system link protocol-processed subhighway data stored in the storage means, processing the read subhighway data according to the frame relay protocol, outputting the processed subhighway data in the unit of data link connection identifiers, extracting the respective subscriber data from the data transferred over the given E1 trunk channel from the inter working function unit and storing the extracted subscriber data in the storage means in the unit of the subscribers; and a high-level data link controller for formatting the data link connection identifier-unit subhighway data processed by the frame relay protocol processor into a high-level data link control format with a specific number of channels, assigning the formatted subhighway data to the specific E1 trunk channel, transferring them to the inter working function unit over an E1 trunk line, deformatting the data transferred over the given E1 trunk channel from the inter working function unit and outputting the deformatted data to the frame relay protocol processor.